Apparatus for metals distillation



Jan. 4, 1949. n. s. cHlsHoLM Er- AL 2,458,253

APPARATUS FOR METALS DISTILLATION Filed nay so, 1945 2 sheets-sheet 1Coo/ing lAir ATTORNEYS Patented Jan. 4, 1949v Ni'r ' STATES PATENT.

ori-ICE APPARATUS Fon METALS DIsTrLLA'rIo'iv Douglas S. Chisholm andThomas Griswold, Jr., Midland, Mich., assignors to The Dow ChemicalMich., a lcorporation of Company, Midland, Delaware This inventionrelates to apparatus for the distillation of metals. It particularlyconcerns improved means for disposing the feed meta1 in the vaporizingzone in the form of a continuously owing thin film.A

' A number of metallurgical processes involve` distilling a desiredmetal from an alloy thereof Application May 30, 1945, Serial No. 59,710

2 claims. (chess- 19) rates can be realized without overheating` thefeed to the point that boiling and its resulting entrain- Y ment ofalloy in the vapor occur. Another object is to provide a still in whichno part of the feed Ialloy can become stagnant, and in which moltenmetals containing solid matter in suspension can with less Volatilemetals. In certain .of these when the alloy is heated drastically. Insuch a be handled without dilculty.

In metallurgical stills according to the invention, the feed alloy isintroduced into a shallow spiral trough which slopes continuously downthe vaporizing section of the still. During its traverse of the trough,the alloy is heated toa distilling case, the action is usually soviolent that there is a serious entrainment of the boiling alloy in theevolving vapors, with a corresponding decrease in the purityof thedistilled product. In designing a still for Vaporizlng metals, then, oneof the ma- `ior problems is to provide means for disposing the feedalloy in a form such that it will Apresent a maximum surface area forthe disengagement of vapor and yet will not be subject to suchoverheating as produces violent boiling.

One solution to `the problem'is to arrange in the vaporizing section ofthe still a number of superposed trays which hold the metal as a series;

of pools through which it flows While it is being heated. Unfortunately,since in this design structural limitations usually require that thetrays be 'of substantial depth, stagnation of apart of the metalAinvariably occurs. In addition, since the ratio of vapor-disengagingsurface of the metal to total metal volume is small in the case of deeptrays, adequate vaporizing rates can only be obl tained either by goingto a still which has a contion to provide an improved metallurgicalstillin which the ratio of vapor-disengaging area to metal volume islarge, sothat high vaporlz'ing temperature and evolves vaporsof thevolatiliza.- ble component rapidly and effectively without undergoingebullition,l Because of the slope of the trough, the' alloy is incontinuousv now at all times while it is being heated. lis a result,4allportions ofthe heated metal are repeatedly brought to thevapor-disengaging surface of the flowing stream to release theirvolatilizable component; stagnation does not occur. In addition, solidparticles entering with the feed are washed through to the outlet by themoving metal; the still is thus to a large extent self-cleaning.

The invention may be further explained'with reference to theaccompanying drawings, in which:

Fig. 1 is a vertical assembly, largely in crosssection, of one form ofmetallurgicalistiil embodying the invention;

Fig. 2 is a vertical cross-section of a portion of the vaporizing zoneofa still embodying another form of the invention; and

Fig. 3 is a fragmentary perspective view of the construction shown inFig. 2. a

The apparatus may be described with reference to the distillation ofmagnesium from a leadmagnesium alloy in which lead preponderates,although it is to be understood that the invention is not thus limited.

In the equipment of Fig. 1, the liquid lead-magnesium alloy to bedistilled is stored in an alloy steel tank 4 surrounded byinsulatingbrick i.

-The alloy is withdrawn by a sump pump 6 driven by' a variable-speedmotorr 1 and is forced through a feed line 8A into the top of thevaporizing section of the still 9. Y

This still is constructed of a large-diameter alloy steel pipe setvertically and provided at the lower end with a conical bottom l0 fromwhich a drain pipe Il extends into the reservoir 4. At

. the upper end, the still is closed' by, a anged dome l2 from which avacuum line I3 leads to an exhaust pump I4, the. line being providedwith a clean-out flange i5. The still is divided into a formed, forconvenience, of three pieces held together by dowels 23. The pillarrests on a graphite plate 24, which ts snugly into vthe bottom piece IUand is provided at its edge with one or more drain holes 25, and issecured at the top by alloy steel hold-down lugs 26 welded tothe wan ofthe stm. A cup 2l is formed in the top of the pillar v22 to receivealloy issuing from the feed pipe 9.

In the side of the pillar 22, there is cut a spiral alloy-carryingtrough 28, starting' at the cup 21 and continuing at a smooth slopeuntil it runs out at the bottom just above the support plate 24. Theprecise cross-sectional shape of the i trough is not critical, but it ishighly desirable that its rdepth be a minor fraction of its width, i. e.that the trough be as shallow as possible. It is likewise preferablethat the downward slope of the trough be gentle, which is achieved bycutting thespiral with a pitch which is a minor fraction of the diametervof the pillar 22, as shown in Fig. 1. The base diameter of the pillarshould ordinarily be nearly equal to the inside diameter of the still,while thetop diameter is preferably a major fraction of the stilldiameter.

Magnesium vapors generated in the Vaporizing section I6 escape upwardlyinto the condensing section I'l, where they come into con-4 tact withthe cooled walls and are condensed to liquid magnesium. The condensateAtrickles down into an vannular collecting gutter 29 welded to the wallof the condenser at the bottom, and from there'runs through a productline 30 into a holding-pot 3l set in brickwork 32 and fired by a gasburner 33.

The alloy tank 4 and condenser ll are provided wth heaters as shown, andthe associated pipes 8, Il and 30 with heaters, not illustrated, toraise them to the appropriate temperatures when beginning operation.These parts are also jacket-ed with thermal insulation, not shown, toprevent freezing of the lead-magnesium alloy and the magnesium productonce circulation is established.

In operation of the apparatus shown in Fig. 1, the lead-magnesium alloyin the tank 4 is kept under a protective saline flux or inert gasatmosphere. The tank'4 and feed line 8 are maintained at a temperatureabove the freezing point of the alloy, preferably at 550 to 600 C. Theburners 28 are adjusted to maintain the lower section I6 of the still ata vaporizing tempera- Y ture, usually 775 to 875 C., and the cooling airto the condenser I1 is controlled so that the temperature 'of themagnesium condensate is above its freezing point (651 C.), preferably655 to 665 C. The lexhaust pump I4 is operated to hold the still at apressure which is suiciently reduced to permit boiling to take'place ata high rate, but is above the vapor pressure of the magnesiumcondensate; absolute pressures between 0.i and about 0.5 inch of mercuryare most satisfactory. At this pressure, the alloy in the feed line 8and the return drain II, and the magnesium in' the product line-30 riseto levels well abovel those of the tank 4 and pot 3l, forming barometricseals.

The motor l is adjusted so that the pump 6 forces lead-magnesium alloyata desired ratev into the still, where it falls into the Icup 21. Thealloy then flows continuously down the convolutions of the spiral trough28 and finally through the openings 25 and out the drain Il, being' atthe same time heated by radiation from the hot wall I6 and by contactwith the pillar 22 which is lself heated by radiation. As thealloypasses ldown the trough 28, part of the magnesium in it isvaporized without appreciable occurrence of ebullition and with little,

if any, entrainment of the alloy. The vapors rise it may be cylindrical,in which case its diameter would have to be considerably less than thatof the still.

The use of graphite or other carbon asa material of construction for thepillar 22 is preferred because of its inertness to thermal shock,

its high emissivity, which is importantv where the pillar is to beheated by radiation, and the fact that it does not corrode withintroduction of undesired substances into the iowing alloy. However, thepillar may, in some instances, be made of other materials, such as alloysteel or ceramic brick.

t In an alternative construction according to the invention, the'spiralmetal-retaining trough, in-

trough assembly is preferably made up of acy- ,i

lindrical sleeve 3 6 which slides snugly into the still and to theinsideof which the spiral strip 35 is welded. The sleeve and associated troughare preferably made up in a number of identical sections which areslipped into Athe still body through the top and are superposed withinthe vvaporizing section of the still to form a continuous spiral troughof any desired height. (One such section is shown in Fig. 2.)

In operation of the still of Figs. 2 and 3, the alloy feed is introducedinto the' upper end of the trough 34 and circles downwardly through thestill, being heated from the hot wall I6 and vaporizing its volatilecomponent, The vapors rise through the open central core and escape intothe .condenser I '1.

It is to be understood that the foregoing description is illustrativerather than strictly limitative, and that the invention is co-extensivein scope with the following claims.

What is claimed is:

1. In a still 4for the vacuum distillation of a volatile metal fromV amolten alloy thereof: a vertical elongated thermally-conductive closedstill body having therein a vaporizing zone and a coninmaenesium from asource not densin-g zone in communication with each other.

. lng the still body at the vaporizing zone for raising the latter to adistilling temperature by heat applied externally to the still body, aconical pillar mounted axially in the still body Within the vaporizingzone and having formed in the outer surface thereof a shallow openspiral trough extending in a continuous downward slope from the upper tothe lower part of the zone, means for introducing the alloy to bedistilled into the upper part of the trough and for collecting residualalloy flowing from the bottom of the trough, and means for withdrawingcondensate from the condenser.

2. A still according to claim 1 wherein the pillar is constructed ofgraphite. v

DOUGLAS S. CHISHOLM.

THOMAS GRISWOLD, JR.

REFERENCES CETED The following references are of record in the fue ofthis patent:

UNTED STATES PATENTS Number Name Date 55,071 Divine et al May 20, 1366503,586 DuPont Aug. 22, 1893 780,475 Behrens Jan'. 17, 1905 l 1,219,413Donk Mar. 13, 1917 1,899,916 Payne Feb. 28, 1933 2,239,371 Osborn Apr.22, 1941 2,309,644 Hansgirg Feb. 2, 1943 2,337,042 Gloss Dec. 21, 19432,362,718 Pidgeon Nov. 14, 1944 2,391,728 McConica Dec. 25, 1945

